The present invention relates to an improvement in a liquid shampoo composition containing an .alpha.-olefin sulfonate as a major component.
Heretofore, there have been employed various anionic surface active agents and nonionic surface active agents as surface active agents constituting liquid shampoo compositions. Of these, anionic surface active agents in the form of a sodium salt or an ethanolamine salt have frequently been employed. Among the anionic surface active agents, an .alpha.-olefin sulfonate possesses high foaming ability and detergency. The .alpha.-olefin sulfonate, however, has a drawback, unlike an alkyl ethoxy sulfate and the like, in that it causes white turbidity at low temperatures because it has inferior stability at low temperatures. For this reason, application of the .alpha.-olefin sulfonate to liquid detergents has been difficult because of its poor commercial value, although the .alpha.-olefin sulfonate possesses superior performance.
Generally, an .alpha.-olefin sulfonate is a mixture containing a hydroxyalkane monosulfonate, an alkene monosulfonate and a small amount of an alkene disulfonate. Each of these components further contains several types of structural isomers. The mixture is recognized as an ".alpha.-olefin sulfonate" in the detergent industry. Since each of the components of the .alpha.-olefin sulfonate has a different crystallization point, the .alpha.-olefin sulfonate causes white turbidity where the component having the highest crystallization point is first allowed to precipitate as crystals at low temperatures. Once it causes white turbidity, the .alpha.-olefin sulfonate is unlikely to be easily returned again to a transparent state.
In order to improve the stability of the .alpha.-olefin sulfonate at low temperatures, it may be considered that a known hydrotrope (a compound possessing the ability to increase the water-solubility of an organic compound) such as ethanol, propylene glycol, glycerin or the like be added. In this case, the effect of depressing the freezing point of water can be recognized. However, not only the effect of improving the stability at low temperatures of the -olefin sulfonate can be little improved, but the free water in the .alpha.-olefin sulfonate is decreased, thereby causing an increase in the amount of crystals precipitated at low temperatures.
As examples of employing an .alpha.-olefin sulfonate demonstrating such defects as hereinabove mentioned as a liquid detergent, British Pat. No. 1,225,218 illustrates examples obtained by adding alkali metal salts, ammonium salts or organic base salts of an alkyl- or alkenyl polyglycol ether carboxylic acid to an .alpha.-olefin sulfonate having 8 to 20 carbon atoms; and U.S. Pat. No. 3,852,221 illustrates examples prepared by adding a substituted fatty acid amido component and a sulfonated hydrotrope component and the like to an .alpha.-olefin sulfonate. In the detergents illustrated in these publications, however, the stabilities at low temperatures of the .alpha.-olefin sulfonates are not improved to a sufficient extent.
With a sense of consumer demand, a liquid shampoo composition has been desired with a function of favorably maintaining conditions after hair washing (smoothness, lack of stickiness and the like) or a conditioning property in combination with the above functions which should be naturally present in shampoos.
Accordingly, it has become important to produce liquid shampoo compositions that have superior conditioning properties and good stability at low temperatures; for example, at -5.degree. C. or lower in winter in accordance with storage conditions.